A laboratory
experiment has given rise to tiny filaments that mimic structures found in ancient
rocks identified as microfossils. The findings cast further doubt over whether
the oldest known microfossils found in the 3.5-billion-year-old Warrawoona Group
in Australia were indeed produced by living organisms, with implications for the
search for early life on Earth and elsewhere.

Field emission scanning electron microscopy
images of twisted filaments made by a purely inorganic mechanism. Image courtesy
of J.M. García-Ruiz.

In experiments reported in the Nov. 14 Science, J.M. García-Ruiz
of the Consejo Superior de Investigacione Cientificas and the University of Granada,
Spain, and Stephen Hyde and his team at the Australian National University, Canberra,
and the Geological Survey of Western Australia, set up conditions where long filaments
and sheets of crystals formed in a high-pH bath, a solution of barium salt and
sodium silicate, at varying temperatures. Focusing on 5- to 10-micron-sized structures
that formed at room temperature, they found a complex composite of inorganic and
organic material, with tiny crystals of organic barium carbonate, enveloped by
silica. After dissolving away the carbonate, the team found that the remaining
hollow structures looked surprisingly like the tiny ropy caterpillar-like structures
imprinted in the Warrawoona rocks.

The laboratory ecosystem was geochemically plausible during the Archean,
García-Ruiz and his co-authors wrote. The required elements  from
an alkaline medium to the presence of low-molecular-weight simple organic molecules
such as phenol or formaldehyde  could have been at hand during the formation
of the Warrawoona, which is rich in chert (SiO2), barite (BaSO4) and carbonate
minerals. No life would have been necessary.

If the Warrawoona microfossils (found in two formations that differ in age by
about 25 million years) are the oldest biological forms on Earth, says Robert
Hazen of the Carnegie Institution of Washington, then that implies life
started very early and easily. If not, then life likely jumpstarted after
the planet was barren for billions of years, which seems as unlikely if not more
so, he says.

Hazen says the new laboratory experiments are promising for future protocols to
identify signatures of life at the microscale. However, he says, the teams
work has an increasing number of special conditions, which is always
disturbing, when trying to apply Occams razor  the solution with the
least number of assumptions.

Theres a tremendous amount at stake here, Hazen says, particularly
for the astrobiology community. If we cant tell on Earth if its
life, how can we go to Mars and determine its life?